[build] Support libgo on Solaris 2

[Eric Botcazou]

> On the golang-dev list there is a bit of a push for sparc64 rather than
> sparcv9.  What does uname -m print on 64-bit SPARC systems?  Is it the
> same or different for Solaris and GNU/Linux?

uname -m returns sparc64 on Linux.  It always returns sparc on Solaris.

sparc64 should be used over sparcv9, the latter is just too confusing.

-- 
Eric Botcazou